04 May 2012

Blonde genes vary around the world

All blondes are not alike, according to a new study that finds different genes dictate flaxen locks in different areas of the globe.

All blondes are not alike, according to a new study that finds different genes dictate flaxen locks in different areas of the globe.

The genetic variant that causes many dark-skinned people from the Solomon Islands to have blonde hair is different from the gene possessed by blonde Europeans, the study found. Researchers from Stanford University School of Medicine found that this particular variant is absent in the genomes of Europeans.

"Since most studies in human genetics only include participants of European descent, we may be getting a very biased view of which genes and mutations influence the traits we investigate," study co-senior author Carlos Bustamante, professor of genetics at Stanford, said. "Here, we sought to test whether one of the most striking human traits, blonde hair, had the same - or different - genetic underpinning in different human populations."

The frequency of blond hair in the Solomon Islands is between 5% and 10%, the researchers said.

"They have this very dark skin and bright blonde hair," study co-senior author Sean Myles, a former Stanford postdoctoral scholar who is now an assistant professor at the Nova Scotia Agricultural College, said in the release. "It was mind-blowing. As a geneticist on the beach watching the kids playing, you count up the frequency of kids with blond hair, and say, 'Wow, it's 5 to 10%'."

How the study was done

Many locals assumed their blonde hair was the result of sun exposure or high fish consumption. Others believed it was a trait passed on by European explorers. The study authors, however, sought to determine if there was a unique genetic basis for this characteristic.

In conducting the study, which is scheduled to be published in the journal Science, the researchers assessed Islanders' hair and skin colour using a light reflectance meter. The investigators also took participants' blood pressure, measured their heights and weights, and collected 1,000 saliva samples from the villagers to examine their DNA.

To look for the genes associated with blond hair, the researchers then selected 43 of the most blonde and 42 of the darkest-haired Islanders from the samples collected, and looked for differences in the frequency of genetic variants between the two groups.

The researchers immediately identified a single signal on chromosome 9, which accounted for 50% of the variance in the participants' blonde hair. They later identified the gene responsible, called TYRP1. The authors noted that the genetic variant that leads to blonde hair among people in the Solomon Islands is not found in the genomes of Europeans.

"Within a week we had our initial result," the study's co-first author, Eimear Kenny, said. "It was such a striking signal pointing to a single gene - a result you could hang your hat on. That rarely happens in science. It was one of the best experiences of my career."

"This is one of the most beautiful examples to date of the mapping of a simple genetic trait in humans," David Reich, a professor of genetics at Harvard University who was not involved in the study, said. The study authors said the finding underscores the need for genetic studies on isolated populations.

"If we're going to be designing the next generation of medical treatments using genetic information and we don't have a really broad spectrum of populations included, you could disproportionately benefit some populations and harm others," Bustamante said.

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